In recent years, an image display apparatus using laser as its light source is attracting attention of being able to display high resolution images in a broad color reproducible range by utilizing the monochromatic property of the laser beam. Moreover, since a laser light source is close to an ideal point light source, collection of light is easier in comparison to a lamp light source. Thus, it is possible to downsize the optical system without deteriorating the light use efficiency, and realize a compact image display apparatus with low power consumption.
Nevertheless, when using a laser beam of a semiconductor laser or the like with high coherency as the light source, generally speaking, glare known as speckle noise in the displayed image becomes a problem upon displaying favorable images. Speckle noise is an interference pattern (hereinafter referred to as the “speckle pattern”) that is created on the retina of the observer due to the high coherency of the laser. It is necessary to reduce the speckle noise in order to display favorable images.
In order to overcome the foregoing problem, attempts have been made for reducing the speckle noise by disposing a light scattering object on a light path between the laser light source of the image display apparatus and the screen, or by forming numerous speckle patterns by disposing and oscillating a diffuser (for example, refer to Patent Documents 1 and 2). As a result of disposing the light scattering object or the diffuser at the optimal position on the light path, or satisfying a given relationship between the particle size of the diffuser and the oscillation speed of the diffuser, the light quantity loss after the laser beam is scattered or diffused can be kept low, and speckle noise can be effective reduced.
Moreover, by disposing a plurality of diffusers and a spatial modulation element on the light path between the laser light source and the screen and disposing at least one among the plurality of diffusers on one end of a diaphragm configured from a magnetic material, it is said that the speckle noise can be reduced by oscillating the diaphragm with the operation of the electromagnet (refer to Patent Document 3).
Moreover, an attempt has been made for reducing the speckle noise by disposing a light tunnel on the light path between the laser light source of the image display apparatus and the screen, causing a laser beam to enter the light tunnel, and oscillating a conical prism for collecting and coupling the laser beams in the light tunnel in a direction that is parallel with the optical axis (for example, refer to Patent Document 4). According to the foregoing configuration, it is said that it is possible to realize multiple reflection which is required for uniformizing the intensity distribution in a short light path length, and reduce the speckle noise by changing the light path of the luminous flux that reaches the screen via an optical system including the conical prism and the like.
Nevertheless, with the conventional technologies described above, there is a problem in that the apparatus needs to be enlarged if a light scattering object is disposed or a motor is used to oscillate the diffuser. Moreover, if a diffuser is disposed at one end of the diaphragm and the diaphragm is oscillated based on the operation of the electromagnet without using a motor, although the apparatus can be downsized, the electromagnet will also become compact as the apparatus is downsized, and there is a problem in that it is difficult to increase the amplitude of the diaphragm. If the amplitude of the diaphragm is small, the reduction effect of the speckle noise cannot be sufficiently yielded. As described above, it was difficult to realize both the downsizing of the image display apparatus and the reduction of the speckle noise with the conventional configurations described above.    Patent Document 1: WO 2005/098532    Patent Document 2: WO 2005/008330    Patent Document 3: Japanese Patent Application Publication No. 2005-301164    Patent Document 4: Japanese Patent Application Publication No. 2008-216923